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Old 08-21-2019, 12:28 PM   #1
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Racor Needle Jumping, Etc

Hello All,
This will be a long one -
I need opinions and advice as to a fuel problem.
I have twin Lehman 135's, with Racors on each. Recently, I replaced my non-working Racor gauges with new, and changed filters.
50 hours or so later, my port Racor gauge began rapidly jumping from zero (around the 5 'o clock position) to what would the 4 'o clock position.

I called a guy, who was obviously busy with something immediate, but he quickly said that it might be a sticking check valve. That's all I got, but I assume that he was referring to a check valve in the injector unit.
He didn't seem too concerned, so I've run that way for maybe 150 hours, with no change (needle still jumping, but in a higher range), and the engine has continued to run well.

I have twin fuel tanks. They run together, and level off if I fuel in just one.
As I last took on fuel, when I took the cap off of the port side, there was a vacuum. Never had that before. The tank vent seems to be clear

This morning, I changed my starboard engine Racor without incident. I loosened the top on the port Racor, and got a phone call that I had to take, which took around an hour. When I returned to the engine room, a small stream of diesel was running from the loose Racor top into the bilge. I couldn't think why there would be fuel pressure, as I hadn't encountered that on previous filter changes. But I did consider that perhaps the higher temperature of the day had caused air in the tank to pressurize, and the tank is close to full. So I opened the fill cap, to see if the leaking diesel would stop, and it didn't.

At this point, I have screwed the Racor top back down, without changing the filter. I wanted to gather my thoughts, and I didn't want to change the filter and have to deal with more flowing fuel.
I can cut off the fuel at the manifold to change the filter, but I've never had to do that in the past.
Could the jumping needle and the supposed check valve issue and the tank vacuum be related? And why is the fuel overflowing out of the top of the Racor?
Thanks to anyone who can weigh in on my problem(s).
Mike
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Old 08-21-2019, 12:51 PM   #2
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Quote:
Originally Posted by wizard View Post
Hello All,
This will be a long one -
I need opinions and advice as to a fuel problem.
I have twin Lehman 135's, with Racors on each. Recently, I replaced my non-working Racor gauges with new, and changed filters.
50 hours or so later, my port Racor gauge began rapidly jumping from zero (around the 5 'o clock position) to what would the 4 'o clock position.

I called a guy, who was obviously busy with something immediate, but he quickly said that it might be a sticking check valve. That's all I got, but I assume that he was referring to a check valve in the injector unit.
He didn't seem too concerned, so I've run that way for maybe 150 hours, with no change (needle still jumping, but in a higher range), and the engine has continued to run well.

I have twin fuel tanks. They run together, and level off if I fuel in just one.
As I last took on fuel, when I took the cap off of the port side, there was a vacuum. Never had that before. The tank vent seems to be clear

This morning, I changed my starboard engine Racor without incident. I loosened the top on the port Racor, and got a phone call that I had to take, which took around an hour. When I returned to the engine room, a small stream of diesel was running from the loose Racor top into the bilge. I couldn't think why there would be fuel pressure, as I hadn't encountered that on previous filter changes. But I did consider that perhaps the higher temperature of the day had caused air in the tank to pressurize, and the tank is close to full. So I opened the fill cap, to see if the leaking diesel would stop, and it didn't.

At this point, I have screwed the Racor top back down, without changing the filter. I wanted to gather my thoughts, and I didn't want to change the filter and have to deal with more flowing fuel.
I can cut off the fuel at the manifold to change the filter, but I've never had to do that in the past.
Could the jumping needle and the supposed check valve issue and the tank vacuum be related? And why is the fuel overflowing out of the top of the Racor?
Thanks to anyone who can weigh in on my problem(s).
Mike
Simple things first....dbl check that fuel tank vents are in fact clear and open.
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Old 08-21-2019, 01:09 PM   #3
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Your lift pumps are creating the high vacuum reading and then at some point something allows fuel or air past some obstruction. It could be a plug in a tank vent, probably the tank that had the vacuum. But it could be a check valve or another obstruction in the fuel lines, or both. It's getting worst judging by the increase in vacuum readings. High vacuum in lines, filters and hoses not designed for the high vacuum will eventually lead to some failure.

Right now it looks like the vent, but the constant change of vacuum could be damaging the tank by flexing the panels, leading to cracks. I'd 1st blow the vents out with air pressure.
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Old 08-21-2019, 01:19 PM   #4
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Leave the fill cap off, run the engine, observe the Racor gauge. This should point you in the right direction..
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Old 08-21-2019, 01:25 PM   #5
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Just a thought on the fuel leaking out of the Racor.... if the height of the fuel filter is lower than that of the fuel in the tank, and the fuel shutoff to the filters isn't closed, gravity can feed fuel into the Racor which could cause that fuel overflow you noticed. Doesn't answer your primary question however.
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